Project Summary Vascular thiol isomerases modify disulfide bonds during thrombus formation in a manner analogous to how serine proteases cleave peptide bonds. Both thiol isomerases and serine proteases accumulate at sites of vascular injury and both are absolutely required for thrombus formation. Yet, while our knowledge of how serine proteases contribute to coagulation is deep, little is known about how thiol isomerases function in thrombosis. And while we have used our knowledge of coagulation factors to develop treatments for thrombotic disease, shortcomings of current antithrombotics in both efficacy and safety indicate a need to leverage new knowledge of alternative mediators of thrombus formation, such as thiol isomerases, for therapeutic benefit. We have identified novel inhibitors of protein disulfide isomerase (PDI) and have demonstrated their efficacy in pre-clinical models. We are currently conducting a phase II/III clinical trial testing the antithrombotic potential one of our PDI inhibitors in the setting of cancer. My research program will focus on the role of thiol isomerases in hemostasis and thrombosis with the objectives of determining the mechanisms by which thiol isomerases contribute to thrombus formation and identifying disease processes in which thiol isomerase-targeted therapies could be used therapeutically. Our studies will transform the field of thiol isomerases in hemostasis and thrombosis by the following advances: (a) a comprehensive understanding of how vascular thiol isomerases participate in thrombosis including how vascular thiol isomerases are regulated, the mechanism by which they act as redox sensors, and the identification of their substrates in thrombus formation, (b) conclusive evidence that thiol isomerases affect hemostasis and thrombosis differently, (c) the identification of coagulopathies and thrombotic diseases in which thiol isomerase-targeted therapies or diagnostics can be used, and (d) the introduction of thiol isomerase-targeted reagents in clinical practice. Over the next 7 years, we will evaluate the role of thiol isomerases in thrombosis associated with sepsis, inheritable hypercoagulable states, anti-phospholipid syndrome, and cancer. This program will thus address the fundamental biology of how thiol isomerases initiate thrombus formation and identify thrombotic diseases in which they participate.